1. Field of the Invention
This invention relates to a piezoceramic shaft-driving type ultrasonic motor which could avoid the electromagnetic interference (EMI) effects caused by the conventional electromagnetic motor, and it overcomes the output torsion disequilibrium in clockwise and counterclockwise rotation of the general ultrasonic motor wherein the rotating speed could be elevated above 3000 rpm and it could be used as the actuator on the biomedical engineering or the cooling fan of the computer CPU.
2. Description of the Prior Art
In the piezoelectric actuator, the piezoelectric ceramics plays important roles wherein the piezoelectric characteristic determines the performance of said actuator. Recently, along with the advance in the piezoelectric material, one of the piezoelectric actuator, the stack type actuator is broadly used in the application of the precise position control. Wherein the ultrasonic actuator of this invention is the mixed mode of bimorph actuator and ultrasonic motor, which adopts the unimorph piezoelectric material as raw materials.
The idea of ultrasonic motor was proposed by the former Soviet scientists wherein the original experimental model of the ultrasonic motor was designed by M. E. Archangelskij, V. Lavrinenko[1] in 1963-64. Later, the papers published by the study field of the ultrasonic motor have diversity study direction as well as study materials; however, most of them are focus upon the ring structure traveling waved type ultrasonic motors. The recently study was classified into the following: by mathematical model deduction, deformation and improvement according to the driving principle, as well as to analyze the vibration mode by utilizing the finite element method, etc [2-9].
For the mathematical model study of the ring-type ultrasonic motor, Oleg Yu. Zharii proposed to use the traveling wave ultrasonic motor as the study object to deduce a set of theory which is used to calculate the rotary speed of the rotor, velocity, the characteristic of piezoelectric, the energy transfer efficiency, etc [10]. By finite element vibration mode analysis [11], J. W. Krome and J. Wallaschek simulate the vibration mode through ANSYS software for the structural deformation as well as betterment. The surface acoustic of noncontact type ultrasonic motor by T.Yamazaki which transmits energy between the stator and rotor and bring the rotor to spin [12]. The noncontact ultrasonic has the better performance in the speed limit compared to that of the conventional contact type ultrasonic motor. Anita M. Flynn utilizes the MEMS technology to fabricate the micro-actuator as the motor stator device on the silicon wafer which ferroelectrics thin-film was fabricated in application to the piezoelectric ultrasonic motors [13].
An object of this invention is to provide a kind of piezoceramic shaft-driving type ultrasonic motor which breaks through the limitation in design of the conventional ultrasonic motor which should rely on the two-phase driving power to construct the traveling wave as well as the high amplitude input A.C. power.
Another object of this invention is to provide a kind of piezoceramic shaft-driving type ultrasonic motor which could avoid the electromagnetic interference effect generated by other conventional electromagnetic devices, and overcomes the phenomena of output torsion disequilibrium in clockwise and counterclockwise running for the general ultrasonic motor wherein the rotating speed could be elevated above 3000 rpm and it could be used in the actuator on the biomedical engineering or the cooling fan of the computer CPU.
The main components of the piezoceramic shaft-driving type ultrasonic motor which could achieve the above-mentioned object of invention are disc type piezoelectric device as the driving stator of the motor which utilizes the pin head above the stator as the dynamic shaft bearing wherein the rotor being drive is contact directly on the bearing with the bottom head of the shaft to transmit the power with friction contact force. The design and fabrication of the motor comprises the stator vibration mode observation and simulation, the measurement of the piezoelectric material impendence frequency response, the mechanical design of the traveling wave, system dynamic identification, the equivalent circuit deduction, as well as the measurement of rotary speed and the rotating torque, etc. The rotating speed of the prototype motor could be reached as high as 3000 rpm on the driving condition of 74 kHz A.C. voltage +/xe2x88x9210Vpp and 0.2 A current wherein the torque is about 0.003 Nxc2x7m. It could be utilized in the driver of the CD, the actuator in the biomedical engineering or the cooling fan in the computer CPU.